Plant biomass is comprised of sugars and represents the greatest source of renewable hydrocarbon on earth. Unlike other renewable energy sources, biomass can be converted directly into liquid fuels. The two most common types of biofuels are ethanol (ethyl alcohol) and biodiesel. Ethanol is an alcohol, which can be produced by fermenting any biomass high in carbohydrates (starches, sugars, or celluloses). Once fermentable sugars have been obtained from the biomass material, these sugars can then be fermented to produce ethanol through a process similar to brewing beer. However, this enormous resource is under-utilized due to the fact sugars are locked in complex polymers, which are often referred to collectively as lignocellulose.
Conventional breakdown of the lignocellulose into monomers (monosaccharides) requires the biomass source material to be softened through chemical and/or physical pre-treatments. Enzymes may also be added that hydrolyze the polymeric forms of sugars contained in the biomass into monosaccharides. Subsequent fermentation can then be carried out utilizing both the 6-carbon and 5-carbon sugars to produce ethanol or other desired bio-products. Sugars generated from the degradation of plant biomass could provide plentiful, economically competitive feedstocks for fermentation into chemicals, plastics, feed additives and fuels.
Carbohydrates constitute the most abundant organic compounds on earth. They are principally found in plants as complex glucose polymers either in the form of cellulose or starch. Cellulose, hemicellulose and glucans make up many structural components of the plant cell wall and woody tissues. These structural components are often complexed with other molecules such as proteins, fats and lignin. Starch is utilized by the plant as a principle storage carbohydrate in seeds and grain consisting of essentially pure linked glucose polymers. Starches are found in many grains as well as in tubers and roots. Starch is a desirable storage carbohydrate due to the fact that it is compositionally simple and can be readily broken down by the plant for energy. Comparatively, lignocellulosic material is composed of glucose and/or several different sugars complexed with lignin. Starch is readily hydrolysable to monomer sugars via effective and inexpensive starch-hydrolysing enzymes whereas lignocellulosic material is neither readily hydrolysable nor relatively inexpensive to process. Carbohydrates are also found in abundance in the form of the simple disaccharide sucrose. Sucrose may be found in crops such as sugarcane, sugarbeets, and sweet sorghum. Unlike sucrose, starch is stable and can be stored in dehydrated form for long periods of time.
It would be desirable to produce a plant that is beneficial for the production of monomer sugars where a higher proportion of carbohydrate is in the form of starch. Methods for creating starch-rich plant biomass and methods for generating free sugars and oligosaccharides from plant biomass as well as use of these free sugars in a biomass conversion method are provided.